A threaded message is one that includes parts of one or more prior messages. A message can be any kind of electronic communication or document. Examples of threaded messages include newsgroups postings, blog dialogs, and response or forwarded emails.
In a threaded message that has many contributors, it often becomes difficult to determine who said what. It is also possible for the sender to change a contributor's contribution, either intentionally or accidentally, without it being evident that something has been changed or what has been changed.
To prevent being mis-quoted or to have their contribution changed in an undesired manner, contributors would like to be able to protect their contributions against unwanted manipulation. While a sender of a message can protect the entire communication by signing it, separately protecting different parts of the message or having different parts “owned” (protected by) different authors does not appear to be possible.
It is possible to use a source-control system to track an email thread. However, issues arise when forwarding messages, quoting text in a reply, having multiple branches in a thread, or having a message which does not quote the previous work at all. Because version control has no concept of a “message”, and assumes change tracking based on a linear progression of changes to a complete file, the random changes in an email thread, cross-quoting, and other activities inherent in messaging do not have clear analogs in version control. In addition, few version control systems have any way of communicating between multiple servers, and maintaining changes between them in an authenticated way.
The change-logging capability of Microsoft Word can be used to show which pieces of a document were edited by whom, and the document may be sent as an attachment to a (blank) email. Not only is this not authenticated, it also suffers from similar problems as the source-control system, as it generally cannot cope with cut-and-paste quoting, multiple branches, or replies with no reference to the original text.
Version-control systems for general software development make it possible to determine who made what changes to a given file. But these tools do not make tracking text through a threaded email simple. Furthermore, detecting that a text fragment (i.e., a quote) was actually sourced from another email is not handled by such tools; an external system of linkages is required (e.g., a convention for checking comments).
XML digital signature-processing rules and syntax provide a mechanism for non-repudiation or encryption of arbitrary fragments of XML. However, they do not easily allow for in-fragment editing of a clear demarcation of a fragment's lineage. They also do not provide a renderer or an editor that could be used by a communications client.